Overwrite repository's labels with organization defaults

[lukecarr]

I've recently decided to adopt Sane GitHub Labels, and configured one of my organizations to use this labelling system by default.

However, these defaults only apply moving forward with new repositories, but I have a bunch of existing repositories that I'd like to start using my new default labels on.

I think having a button to clear all current labels on a repo and replace them with the organization defaults would be really handy for this exact scenario.